Stationary film mercury cell

ABSTRACT

IN A CONVENTIONAL MERCURY CELL FOR PRODUCING CHLORINE AND SODIUM HYDROXIDE FROM BRINE, THE MERCURY FLOWS THROUGH THE CELL DURING ELECTROLYSIS AND PICKS UP SODIUM TO FORM AN AMALGAM. THE AMALGAM LEAVES THE CELL AND IS PUMPED OR ALLOWED TO FLOW THROUGH A SEAL INTO A DECOMPOSER OR &#34;DENUDER&#34; WHICH IS SEPARATE FROM THE CELL. IN THE PRESENT INVENTION BOTH THE ELECTROLYSIS OF THE BRINE AND THE DECOMPOSING OF THE AMALGAM ARE CARRIED OUT IN THE SAME CELL. THE INVENTION IS BASED UPON THE UTILIZATION OF A STATIONARY FILM OR LAYER OF MERCURY AND A NONAMALGAMABLE, ELECTRICALLY CONDUCTIVE, POROUS MEMBER SUCH AS GRAPHITE WHICH IS IN DIRECT CONTACT WITH THE BOTTOM OF THE MERCURY LAYER.

1972 P. CARR 3,682,797

STATIONARY FILM MERCURY CELL Filed 001;. 2, 1970 f o o 0 o c o o o o o o0 o o o o O O O g9af a 0 0 v o o o 0 o o O a o o v\ p o a o o c Q 0 O OO r o 0 o a /c I o a o o o o o o a O a o o o o o O O O O O O o 0 G i {x0 o 0 o a O [V 91 a INVENTOR.

PETER CARR United States Patent Office 3,682,797 Patented Aug. 8, 19723,682,797 STATIONARY FILM MERCURY CELL Peter Carr, Youngstown, N.Y.,assignor to Great Lakes Carbon Corporation, New York, N.Y. Filed Oct. 2,1970, Ser. No. 77,558 Int. Cl. C01d 1/12; C01f 11/14; C22d 1/04 US. Cl.20499 20 Claims ABSTRACT OF THE DISCLOSURE In a conventional mercurycell for producing chlorine and sodium hydroxide from brine, the mercuryflows through the cell during electrolysis and picks up sodium to forman amalgam. The amalgam leaves the cell and is pumped or allowed to flowthrough a seal into a decomposer or denuder which is separate from thecell. In the present invention both the electrolysis of the brine andthe decomposing of the amalgam are carried out in the same cell. Theinvention is based upon the utilization of a stationary film or layer ofmercury and a nonamalgamable, electrically conductive, porous membersuch as graphite which is in direct contact with the bottom of themercury layer.

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to a method and apparatus for the electrolysis of an electrolytesolution of an alkali or suitable alkaline earth metal salt, typically abrine solution of sodium chloride. The invention more specificallyrelates to a special type of mercury cell for carrying out the foregoingelectrolysis in order to produce anode electrolysis products, e.g.chlorine, and alkali or suitable alkaline earth metal reaction products,e.g. sodium hydroxide.

(2) Description of the prior art In a conventional mercury cell forproducing chlorine and sodium hydroxide, the mercury is polarized as acathode in a strong brine solution against a graphite anode, adimensionally stable anode or a porous flowthrough graphite. The mercuryflows through the cell during electrolysis and picks up alkali metalcations (most commonly sodium) to form an amalgam. The alkali metalcontent of the amalgam cannot be allowed to increase beyond a certainmaximum concentration before the amalgam ceases to function etlicientlyand hydrogen and caustic alkali are liberated within the cell. In theconventional mercury cell, however, before this limiting concentrationis reached the amalgam exits from the cell and is pumped or allowed toflow through a seal into a decomposer or denuder which is separate fromthe cell. The decomposer is usually a vessel packed with graphite, orgraphite and iron, through which the amalgam can flow and where it cancome into contact with purified water. An exothermic reaction occurswithin the decomposer between the amalgam and the water to producehydrogen and caustic alkali leaving behind an amalgam denuded of most ofits alkali metal content. This denuded amalgam, i.e. mercury is thenpumped back to the electrolysis cell and the cycle of operationsrepeated.

In such a conventional mercury cell system substantial amounts ofmercury are necessary to operate the cell. A mercury circulating pumpand a separate decomposer or denuder is also necessary for each cell. Itis also necessary to have the bottom of the cell tilted at a slightangle in order to obtain the desired mercury flow.

SUMMARY OF THE INVENTION The invention described herein consists ofbasically the same brine flow, anode arrangement and mercury cathodesystem as is found in conventional cells. However, no re-circulating ofthe mercury (or alkali metal amalgam) is carried out but instead theseare stationary.

By stationary is meant that the mercury or the amalgam are not pumped orallowed to flow through a seal into a separate decomposing or denudingcompartment as is common in a conventional mercury cell. Also, insteadof the mercury being situated upon a steel, rubberized steel, or othersolid bottom, the mercury rests on a porous plate or base. The porousplate has to be of a porosity which cannot be penetrated by the mercuryor mercury amalgam under cell conditions but which can be permeated bypurified water, steam or other alkali or alkaline earth metal oxidant.The porous material must also be essentially non-amalgamable withmercury, (i.e., a material which does not form an alloy with themercury), stable to an alkaline and hydrogen environment, not have ahigh hydrogen overvoltage (whereby decomposition of amalgam would onlyoccur slowly), and must also be a conductor of electricity so that itcan act as a cathode in the decomposition reaction. Porous graphite,more fully described hereinafter, fulfills these requirements.

On the opposite side of the porous plate, below the mercury cathode, acompartment is fabricated, so that an alkali or alkaline earth metaloxidant, such as purified water or steam, can be led into the porouscell base. This is facilitated by applying a vacuum to the cell base.This vacuum must be suflicient to draw the alkali or alkaline earthmetal oxidant through the pores to enable it to come into contact withthe amalgam at the porous base/ amalgam interface while not being a highenough vacuum to draw the mercury or amalgam cathode through the porousbase. It has been found that reducing the absolute pressure to only 730mm. of mercury is sufficient to draw over the oxidant, e.g. water orsteam, without drawing the mercury or amalgam through the pores of aporous graphite cell base. A vacuum of 700 mm. of mercury is morepreferred and this may typically be increased, without adverse results,to as low an absolute pressure as 500 mm. of mercury.

During operation of the cell the water in the pores at the porousbase/amalgam interface reacts with the amalgam to form hydrogen andcaustic alkali, which are drawn off from the base by the vacuum. Theamalgam is therefore being continually denuded of its alkali or alkalineearth metal content and continues to operate efliciently withouthydrogen evolution in the upper compartment situated over the mercury.In a system such as this there is a considerable reduction in the amountof mercury necessary to operate the cell, Less than 12 pounds of mercuryis needed for every 1000 amperes capacity the cell has, rather than the50 pounds or so that is presently required in a conventional mercurycell. With the mercury not being circulated the need for mercurycirculating pumps and separate decomposers is eliminated. A singlevacuum pump is typically sufiicient to operate the denuding aspect of aWhole cell room.

In accordance with the foregoing, therefore, it is an object of thepresent invention to considerably reduce the mercury inventory neededfor the operation of a mercury cell.

Other objects are to:

Reduce the mercury loss associated with conventional denuding practice;

Eliminate the need for a mercury circulating pump on each cell;

Eliminate the need for a separate decomposer for each cell;

Eliminate the need to have the cell tilted at a slight angle in order toprovide mercury flow;

Eliminate ripples in the mercury normally present in the flowingmercury, thereby allowing closer anode and cathode spacing, reducingoperating costs; and to Eliminate the need for weirs within theelectrolyzer to prevent brine llowing out with the mercury.

Additional objects of the invention will become apparent from thedetailed description of the invention which follows.

DESCRIPTION OF THE DRAWING Details of the cell of the present inventionare shown in FIGS. 1 and 2. FIG. 1 is a vertical sectional view of thecell. FIG. 2 is a horizontal sectional view taken across the plane 2-2of FIG. 1. With reference to FIG. 1, the cell, indicated generally bythe numeral 1, may be considered as comprising two distinct reactioncompartments, upper compartment I and lower compartment H. The cell top1a, bottom 1b, and sidewalls 1c, are all constructed of suitablenon-electrically conductive, chemically inert material, or lined with amaterial 1d (such as rubber) possessing these properties.

The two compartments are separated by a stationary, substantiallyhorizontal mercury cathode layer 2. Compartment I contains anelectrolyte solution 3 of an alkali or suitable alkaline earth metalsalt, such as a brine solution of sodium chloride to be electrolyzed; anelectrolyte inlet means 4 and electrolyte outlet means 5. (Suitablealkaline earth metal salts refer to salts of calcium, barium andstrontium.) Outlet means 5 may also be used to draw off anodeelectrolysis products (such as chlorine). Compartment I also contains atleast one anode 6 (such as graphite), so positioned above the mercurycathode layer 2 as to form a suitable electrode gap between the anodeand the mercury cathode layer. (FIG. 1 is illustrative only and shouldnot be interpreted as drawn to scale with respect to this gap, or thethickness of the cathode layer 2, or the thickness of lining material1d.) Compartment II, below the mercury, contains an electricallyconductive, porous, non-amalgamable member 7, such as porous graphite,which is in direct contact with the bottom of the mercury layer 2, andwhich supports same. The compartment II also contains inlet means 8 and8a for introducing an oxidant (such as steam) of the alkali or alkalineearth metal into and through the porous member 7, and outlet means 9 forremoving reaction products resulting from the reaction between the metaloxidant ,(e.g. steam) and the alkali or alkaline earth metal amalgamproduced in reaction compartment 1.

The lower compartment has means for applying a slight vacuum to theunderside of the porous, electrically conductive support member 7.Conduit 9 may be used both to remove reaction products and to applyvacuum. The potential between the anode and the cathode is applied byelectrical connections 10a and 10b made to the anode and cathode,respectively. The electrical connection to the mercury cathode maytypically be made through the electrically conductive, porous memberwhich is beneath and in contact with the mercury cathode layer. Thevacuum is applied by means of a vacuum pump (not shown) which applies avacuum to the underside of the porous, electrically conductive supportmember through conduit 9 and vacuum pores 9a, thereby assisting indrawing the steamthrough the porous graphite and also in removingreaction products from the lower compartment of the cell. The poroussupport member is permeable to the steam (or alkali or alkaline earthmetal oxidant) but is impermeable to the mercury under the celloperation conditions, which refer particularly to the temperatures usedand the amount of vacuum employed.

A metal base 11, typically made from steel and shown in horizontalsection in FIG. 2, is preferably employed beneath the porous graphitemember 7 in order to help support same and also to conveniently providesteam access holes 8a and vacuum pores 9a to facilitate introduction ofthe steam or metal oxidant and removal of the reaction products from thelower compartment. Typically the conductive porous member 7 and themetal base 11 will be made integral by cementing them at their adjoiningfaces thus helping to insure optimum and fixed location of holes 8a and9a and also minimum voltage loss across this portion of the electricalcircuit. (As indicated in FIG. 1, the electrical connection 10b to themercury cathode is typically made directly to the metal base and thenthrough the electrically conductive porous member 7). A goodelectrically conducting cement 12, resistant to the reactants andreaction products of the cell, such as a graphite filled epoxy cement,is therefore desirably employed to make an electrically conductivecomposite support for the mercury cathode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrolytic cell wasconstructed having the features shown in the drawings. As previouslypointed out the cell had two particularly unique features; first themercury pool rested on a porous graphite base rather than the steel basecommon in commercial mercury cells; and second, the mercury or amalgampoll was stationary or confined in place rather than being pumped out ofthe cell recirculated through a decomposer and back to the electrolyzeras is common in conventional systems. Voltages between the decompositionpotential of the alkali or alkaline earth metal salt being electrolyzedand about 6 volts, and current densities of up to l ampere per squarecentimeter (amp./sq./cm.) (or 10,000 amps per square meter, which iscomparable with cathode current densities now used in industrialpractice in electrolyzing NaCl brine) were applied to the cathode withsuccessful denuding of the amalgam formed being obtained. It most of thetests conducted, sodium chloride brine solution was the saltelectrolyzed; the anode used was fabricated from normal densitygraphite, the cell operated at temperatures between 70 C. and C., andthe electrolyte pH ranged from 1.9 to 2.5. Steam was used as the metaloxidant. (By oxidan is meant a material which is chemically reduced bythe alkali or alkaline earth metal of the amalgam).

A vacuum of 700 mm. (Hg) was employed and this was suflicient to drawover the water (steam which condensed at the interface of the mercurylayer and the porous graphite) without drawing the mercury through thepores of the porous graphite. During operation of the cell the Water inthe pores at the interface reacted with the sodium amalgam (aspreviously mentioned, the mercury changes to amalgam) to form hydrogenand caustic soda solution which were drawn off from the graphite by thevacuum. The slight vacuum prevented any hydrogen from going up throughthe thin mercury film. The amalgam was therefore being continuallydenuded of its alkali metal content and continued to operate efficientlyin the electrolyzer (compartment 1) without hydrogen evolution in thatcompartment. The current density coupled with the weight of mercuryemployed diciated a total mercury requirement of only 12 lbs. for every1000 amps capacity the cell had and is to be compared to the 50 lbs. ormore of mercury required for operation of a conventional mercury cell.As a result of this the present invention offers the capital advantageof massive reduction in the mercury inventory. The operating voltages ofthe cell were not affected by the stationary film principle. With inplace regeneration of the mercury and the mercury not being circulated,the need for mercury circulating pumps and separate decomposers waseliminated.

It should also be noted that in the operation of mercury cells, metallicimpurities such as V, Mo, Cr, Ti, Ta, (Mg

and Fe), Ni, Co, Fe and W, cause premature amalgam decomposition in theelectrolysis compartment and have to be removed from the feed brinebefore it enters the cell. These impurities are excellent decompositioncatalysts when added to the porous graphite of the present invention andgreatly improved the denuding characteristics of the described system.These impurities can be deposited on the porous graphite by variousestablished metallizing techniques or their salts can simply be added tothe denuding steam or water to be carried to the amalgam/porous graphiteinterface where they catalyze the decomposition of the amalgam. With thesaid catalytic materials present, cathode current densities in excess ofl amp/sq. cm. or 10,000 amps per square meter can be attained withoutamalgam decomposition within the electrolysis compartment (compartmentI).

In the stationary film mercury cell working at commercial cathodecurrent densities the decomposition of amalgam occurs rapidly withoutmuch sodium buildup in the mercury. This especially true when metallicimpurities are present at the amalgam/porous graphite interface. Lessthan 0.02 sodium was found in the amalgam at cathode current densitiesof up to 1 amp/sq. cm. In conventional mercury cells the concentrationof sodium in the amalgam ranges from 0.01% in the inlet to 0.35% at theoutlet. This increase in sodium concentration results in a 150 mv.increase in cathode reversible EME, going from 1.68 volts at 0.01%sodium to 1.83 volts for the 0.35% sodium concentration, all at 80 C. in250 gm./l. sodium chloride. With the present stationary film mercurycell having a sodium concentration in the amalgam approximately that ofthe inlet end of a conventional mercury cell a voltage saving of around90 mv. is gained over a conventional mercury cell having an average of0.17% sodium in the mercury.

A further benefit of having a low sodium concentration in the mercury isthat the level of metallic impurities that can be tolerated in the feedbrine can be increased Without an excessive amount of hydrogen beinggenerated. On the other hand, if the impurities are kept at the lowlevel used in current mercury cell practice, then, because of the lowsodium level in the amalgam, the amount of hydrogen generated in thecell is lowered. This is beneficial both from a safety point of view andby increasing the sodium hydroxide current efliciency.

A considerable loss in current efficiency in conventional mercury cellsis attributed to the following reactions:

Na(Hg)-|- /z C1 (at the cathode)=NaCl-|- (Hg) Na(Hg)+HCl (at thecathode)=NaCl+ /zH (Hg) These reactions combined results inapproximately a 5% loss in current efi'iciency. Using the stationaryfilm mercury cell of this invention, the rates of these reactions areconsiderably reduced because of the low sodium concentration in theamalgam. This results in further increased operating efficiency for thecell.

The production of strong sodium hydroxide solution (IO-50% by weight) ina single pass through the porous graphite necessitates the use ofrelatively small quantities of denuding water. It is important,therefore, that almost all the water added migrate to the porousgraphite/amalgam interface, to continue an eflicient denuding of theamalgam. A preferred method of doing this is to feed steam, rather thanwater, into and through the porous graphite. The large volume of steamproduced from a given volume of water ensures an even distribution ofwater vapor in the porous graphite, thus preventing areas of undenudedamalgam which can occur if water is used, and there is some preferentialchanneling of water through the porous graphite. Also, as previouslyindicated, the cell temperature will generally be kept below 100 C. As aresult there is a tendency for much of the steam to condense out at theamalgam/ porous graphite interface which is precisely where the water isneeded for efficient denudmg.

To provide for the desired denuding action and also fairly even steam(and/or water) distribution into and through the porous graphite, it isdesirable that the porous plate be not too thick and also that itsporosity characteristics be closely controlled. Toward these ends, afine carbon aggregate mix having a maximum grain size of 0.01 inch willtypically be employed in making the porous graphite body, and thethickness of graphite body used will typically be between about 0.25 andabout 0.05 inch, with a thickness of about 0.1 inch preferred.

As a guide to the characteristics of the porous graphite support memberemployed in the present invention and for purposes of comparison, thefollowing table is set forth, showing typical properties of porous,normal and high density graphite.

High Type graphite Porous Normal density Apparent density, g./cc 0.96 1. 60 1. 68 Permeability, darcys:

X 32 0. 0601 0. 029 Y 32 0. 0485 0. 029 Z 32 0. 0754 Permeability of air7 0. 01 0. 006 Permeability of water 13 0. O2 0. 012 Total accessibleporosity, percent 44 22 17 Average pore diameter, 4 u 45 7 9 Maximumgrain size, inches..- 0. 008 0. 0328 0. 0328 Youngs modulus sonic methoWG 5 1.4Xi0" 1. 3x10 AG Tensile strength:

WG, p.s.i

p.s.i Flexurai strength, WG, p.s.i (3d point loading) AG, p.s.iCompressive strength- G, p.s.i AG, p.s.i Electrical resistivity, WG,ohm-inches 1 Z direction is parallel to direction of extrusion ormolding; X and Y direlctians are perpendicular to direction of moldingor extrusion and to eac 0 er.

1 Cubic feet of air per minute passing in the Y direction through asquare foot of area one inch thick at 2 inches of water pressure.

8 Gallons of water per minute passing in the Y direction through asquare foot of area one inch thick at 6 p.s.i.

4 A volume-weighted average. 5 WG=Test specimens cut with their longdimension with the grain; AG=Test specimens cut with their longdimension against the grain.

= .19 p.s.i. 10. b .17 p.s.i.X10.

4, 500 470 1l0X10- 30Xl0- 26X10- The porous graphite member employed inthe present invention will preferably possess an apparent densitybetween about 0.8 and about 1.2 grams per cubic centimeter, an averagepore diameter between about 30 and about 150 microns, typically 50microns, a permeability in darcys in the X, Y and Z directions of atleast about 10 darcys, and a total accessible porosity of at least about30%.

The porous, non-amalgamable member must be electrically conductive sothat the lower compartment can act as a short-circuited battery with theamalgam acting as anode, the porous member acting as cathode forhydrogen discharge, and the lower compartment reaction products actingas electrolyte, with some sites on the porous member forming theshort-circuit from the cathode to the amalgam anode. Porous graphitehaving an electrical resistivity typically between about and about x 10*ohm-inches is preferred for this purpose.

Electrolyte solutions of alkali metal salts other than of sodiumchloride may be employed in the present invention, particularly brinesof alkali metal halides, for example, of potassium chloride and lithiumchloride, and solutions of other alkali metal salts such as of sodiumsulfate. Electrolyte solutions of suitable alkaline earth metal salts,such as the chlorides of calcium, strontium and of barium, may also beemployed.

Decomposing fluids or oxidants other than water or steam (or togetherwith water or steam) also can be employed. Aqueous and non-aqueoussolutions of oxidants can be employed. For example, water or steam andcarbon dioxide in combination may be employed as the oxidant, in whichcase a reaction product would be an alkali or alkaline earth metalcarbonate; methyl alcohol may be used as the oxidant in the electrolysisof a sodium salt in which case a reaction product would be sodiummethylate; or an aqueous polysulfide solution may be employed as theoxidant in the electrolysis of a sodium salt in which case a reactionproduct would be sodium sulfide.

In addition to the previously indicated objects, the attainment of whichrepresent many general advantages of the present invention, it shouldalso be noted that the cell of this invention also olfers severalspecific advantages over conventional mercury cells, including thefollowing:

(a) The low average sodium concentration in the amalgam compared toconventional mercury cells lowers the cathode reversible EM andovervoltage giving rise to a voltage saving;

(b) The impurity level in the feed brine can be increased withoutincreasing hydrogen evolution above its present level;

With a pure feed brine, the amount of hydrogen evolved from the cathodeand discharged with the chlorine is reduced, increasing both safety andsodium hydroxide current efliciency; and

(d) The substantial loss in current efliciency in conventional mercurycells, due to chlorine reacting with the amalgam, is reduced, due to thelow sodium concentration in the amalgam. This also results in anincrease in current efliciency.

The foregoing describes my invention but I intend to be limited only bythe scope of the appended claims.

'I claim:

1. A method for the electrolysis of an electrolyte solution of an alkalior suitable alkaline earth metal salt wherein said electrolysis iscarried out in an electrolytic cell comprising two distinct reactioncompartments separated by a stationary, substantially horizontal layerof mercury, said method including the steps of:

(a) Introducing the electrolyte solution into an upper compartmenthaving a mercury cathode layer and at least one anode positioned abovesaid layer to form a suitable electrode gap;

(b) Applying a potential between the anode and the cathode whereby theelectrolyte is decomposed to liberate the anode electrolysis products atthe anode and the alkali or alkaline earth metal is deposited into themercury cathode to form the alkali or alkaline earth metal amalgam;

(c) Withdrawing the electrolyte and the anode electrolysis products fromsaid upper compartment;

(d) Introducing an oxidant for said alkali or alkaline earth metal intoa lower compartment below the mercury through an electricallyconductive, porous, nonamalgamable member which is in direct contactwith the bottom of the mercury layer and which supports same, saidporous support member being permeable to the oxidant but impermeable tothe mercury under the cell operating conditions;

(e) Reacting said oxidant for said alkali or alkaline earth metal withthe metal amalgam produced in the upper compartment; and

(f) Removing the reaction products from said lower compartment byapplying a vacuum to the underside of said porous, electricallyconductive support member.

2. A method according to claim 1 wherein the electrolyte solution is anaqueous solution.

3. A method according to claim 1 wherein the reaction step (e) iscarried out in the presence of an amalgam decomposition catalyst.

4. A method according to claim 1 wherein the potential is applied bymeans of suitable electrical connections made to the anode and to themercury cathode through the electrically conductive, porous member.

5. A method according to claim 1 wherein the potential applied betweenthe anode and the cathode is between the decomposition potential of thealkali or alkaline earth metal salt and about 6 volts.

6. A method according to claim 1 wherein the vacuum applied to theunderside of the porous, electrically conductive support member isbetween about 500 and 730 mm. of mercury.

7. A method according to claim 1 wherein the electrolyte solutionemployed is of a sodium salt, wherein the oxidant is methyl alcohol, andwherein the reaction products removed in step (f) include sodiummethylate.

8. A method according to claim 1 wherein the electrolyte solutionemployed is of a sodium salt, wherein the oxidant is an aqueouspolysulfide solution and wherein the reaction products removed in step(f) include sodium sulfide.

9. A method according to claim 1 wherein the said porous member isporous graphite.

10. A method for the electrolysis of an aqueous electrolyte solution ofan alkali or suitable alkaline earth metal salt wherein saidelectrolysis is carried out in an electrolytic cell comprising twodistinct reaction compartments separated by a stationary, substantiallyhorizontal layer of mercury, said method including the steps of:

(a) Introducing the aqueous electrolyte solution into an uppercompartment having a mercury cathode layer and at least one anodepositioned above said layer to form a suitable electrode gap;

(b) Applying a potential between the anode and the cathode whereby theelectrolyte is decomposed to liberate the anode electrolysis products atthe anode and the alkali or alkaline earth metal is deposited into themercury cathode to form the alkali or alkaline earth metal amalgam;

(c) Withdrawing the electrolyte and the anode electrolysis products fromsaid upper compartment;

(d) Introducing an oxidant for said alkali or alkaline earth metalcomprising water or steam into a lower compartment below the mercurythrough an electrically conductive, porous, non-amalgamable member whichis in direct contact with the bottom of the mercury layer and whichsupports same, said porous support member being permeable to the oxidantbut impermeable to the mercury under the cell operating conditions;

(e) Reacting said oxidant for said alkali or alkaline earth metal withthe metal amalgam produced in the upper compartment; and

(f) Removing the generated reaction products from said lower compartmentby applying a vacuum to the underside of said porous, electricallyconductive support member.

11. A method according to claim 10 wherein the oxidant introduced instep (d) is water or steam alone and wherein the reaction productsremoved in step (f) are hydrogen and an alkali or alkaline earth metalhydroxide.

12. A method according to claim 10 wherein the oxidant introduced instep (d) includes some carbon dioxide and wherein the reaction productsremoved in step (t) include an alkali or alkaline earth metal carbonate.

13. A method for electrolysis of sodium chloride brine wherein saidelectrolysis is carried out in an electrolytic cell comprising twodistinct reaction compartments separated by a stationary, substantiallyhorizontal layer of mercury,.said method including the steps of:

(a) Introducing the brine into an upper compartment having a mercurycathode layer and at least one anode positioned above said layer to forma suitable electrode gap;

(b) Applying a potential between the anode and the cathode whereby thebrine is decomposed to liberate chlorine at the anode and sodium isdeposited into the mercury cathode to form sodium amalgam;

(c) Withdrawing sodium chloride brine and chlorine from said uppercompartment;

((1) Introducing water or steam into a lower compartment below themercury through an electrically conductive, porous, non-amalgamablemember which is in direct contact with the bottom of the mercury layerand which supports same, said porous support member being permeable towater and steam but impermeable to the mercury under the cell operatingconditions;

(e) Reacting said water or steam with the sodium amalgam produced in theupper compartment; and

(f) Removing the generated hydrogen and sodium hydroxide solution fromsaid lower compartment by applying a vacuum to the underside of saidporous, electrically conductive support member.

14. An electrolytic cell for the electrolysis of an electrolyte solutionof an alkali or suitable alkaline earth metal salt comprising twodistinct reaction compartments separated by a stationary, substantiallyhorizontal layer of mercury, said reaction compartments comprising:

(a) an upper compartment for containing the electrolyte solution, saidupper compartment having a mercury cathode layer, at least one anodepositioned above said layer to form a suitable electrode gap, means forintroducing the electrolyte and means for withdrawing the electrolyteand anode electrolysis products; and

(b) a lower compartment below the mercury having an electricallyconductive, porous, non-amalgamable member which is in direct contactwith the bottom of the mercury layer and which supports same, means forintroducing an oxidant for said alkali or alkaline earth metal into andthrough said porous member, and means for removing reaction productsresulting from the reaction between the oxidant and the metal amalgamproduced in the upper compartment, said porous member being permeable tothe metal oxidant but impermeable to the mercury;

said cell also having means for applying a potential beween the anodeand the cathode, and means for applying a vacuum to the underside ofsaid porous, electrically conductive support member.

15. An electrolytic cell according to claim 14 wherein the said porousmember is porous graphite.

16. An electrolytic cell according to claim 14 wherein said poroussupport member is structurally supported on its underside by aperforated metal base.

17. An electrolytic cell according to claim 16 wherein the upper face ofthe metal base is attached to the underside of the porous support memberby means of an electrically conductive cement.

18. An electrolytic cell for the electrolysis of an aqueous electrolytesolution of an alkali or suitable alkaline earth metal salt comprisingtwo distinct reaction compartments separated by a stationary,substantially horizontal layer of mercury, said reaction compartmentscomprising:

(a) an upper compartment for containing the electrolyte solution, saidupper compartment having a mercury cathode layer, at least one anodepositioned above said layer to form a suitable electrode gap, means forintroducing the electrolyte and means for withdrawing the electrolyteand anode electrolysis produced; means in said compartment for applyingan externally applied electrical potential between the anode and thecathode whereby the electrolyte is decomposed to liberate the anodeelectrolysis products and the alkali or alkaline earth metal isdeposited into the mercury cathode to form the corresponding amalgam;and

(b) a lower compartment below the mercury wherein an oxidant for saidalkali or alkaline earth metal is introduced into and through anelectrically conductive, porous, non-amalgamable member which is indirect contact with the bottom of the mercury layer and supports same,said porous support member being permeable to the oxidant butimpermeable to the mercury under the cell operating conditions, whereinsaid oxidant reacts with the metal amalgam produced in the uppercompartment, and wherein said reaction products are drawn oil from saidlower compartment by means of a vacuum applied to the underside of saidporous, electrically conductive support member.

19. An electrolytic cell for the electrolysis of an aqueous electrolytesolution of an alkali or suitable alkaline earth metal salt comprisingtwo distinct reaction compartments separated by a stationary,substantially horizontal layer of mercury, said reaction compartmentscomprising:

(a) an upper compartment for containing the electrolyte solution, saidupper compartment having a mercury cathode layer, at least one anodepositioned above said layer to form a suitable electrode gap, means forintroducing the electrolyte and means for withdrawing the electrolyteand anode electrolysis products; means in said compartment for applyingan externally applied electrical potential between the anode and thecathode whereby the electrolyte is decomposed to liberate the anodeelectrolysis products and the alkali or alkaline earth metal isdeposited into the mercury cathode to form the corresponding amalgam;and

(b) a lower compartment below the mercury wherein an oxidant for saidalkali or alkaline earth metal comprising water or steam is introducedinto and through an electrically conductive, porous, non-amalgamablemember which is in direct contact with the bottom of the mercury layerand supports same, said porous support member being permeable to theoxidant but impermeable to the mercury under the cell operatingconditions, wherein said oxidant reacts with the metal amalgam producedin the upper compartment, and wherein the generated reaction productsare drawn off from said lower compartment by means of a vacuum appliedto the underside of said porous, electrically conductive support member.

20. An electrolytic cell for the electrolysis of sodium chloride brinecomprising two distinct reaction compartments separated by a stationary,substantially horizontal layer of mercury, said reaction compartmentscomprising:

(a) an upper compartment for containing the brine, said uppercompartment having a mercury cathode layer, at least one anodepositioned above said layer to form a suitable electrode gap, means forintroducing the brine, and means for withdrawing brine and chlorine;means in said compartment for applying an externally applied electricalpotential between the anode and the cathode whereby the brine isdecomposed to liberate chlorine at the anode and sodium is depositedinto the mercury cathode to form sodium amalgam; and

'(b) a lower compartment below the mercury wherein water or stream isintroduced into and through an electrically conductive, porous,non-amalgamable member which is in direct contact with the bottom of themercury layer and supports same, said porous support member beingpermeable to water and steam but impermeable to the mercury under thecell operating conditions, wherein said water or steam react with thesodium amalgam produced in the upper compartment, and wherein thehydrogen and sodium hydroxide solution generated are drawn olf from saidlower compartment by means of a vacuum 11 12 applied to the underside ofsaid porous, electrically 1,368,955 2/1921 Matsushima 204251 conductivesupport member. 1,981,498 11/1934 Engelhardt et a1. 204-251 ReferencesCited JOHN H. MACK, Primary Examiner UNITED STATES PATENTS 5 D. R.VALENTINE, Assistant Examiner 735,564 8/1903 Byrnes 204219 1,109,3119/1914 Allen e 204-99 1,336,281 4/1920 Cataldi 204251 GR 204-100, 128,219, 250, 277, 278

